The problem is, that library usually does not provide good enough boundaries. C library can just shit over your process memory. Java library can cause all the hell over your objects with reflection, can just call System.exit(LOL). Minimal boundary to keep demons at bay is process boundary and you need some way for processes to talk to each other. If you're separating components into processes, it's very natural to put them to different machines, so you need your IPC to be network calls. One more step and you're implementing REST, because infra people love HTTP.

>Requiring every component to be behind a network call seems like overkill in nearly all cases

That’s what I was referring to, sorry for the inaccurate adjective.

Most people try to split a monolith in domains, move code as libraries, or stuff like that - but IMO you rarely avoid a shared space importing the subdomains, with blurry/leaky boundaries, and with ownership falling between the cracks.

Micro services predispose better to avoid that shared space, as there is less expectation of an orchestrating common space. But as you say the cost is ridiculous.

I think there’s an unfilled space for an architectural design that somehow enforces boundaries and avoids common spaces as strongly as microservices do, without the physical separation.

In general, my experience is "the more moving parts == less reliable", if I were to generalize across two decades of running web services. The most reliable platforms I've helped manage has been platforms that tried to avoid adding extra complexity until they really couldn't avoid it, and when I left still deployed applications by copy a built binary to a Linux host, reload the systemd service, switch the port in the proxy and let traffic hit the new service while healtchecking, and when green, switch over and stop the old service.

Deploys usually took minutes (unless something was broken), scaling worked the same as if you were using anything else, increase a number and redeploy, and no Kubernetes, Docker or even containers as far as the eye could see.